A good question.
A local answer.

Check the accommodation's kitchen and barbecue equipment, then see which groceries are available on the island for your dates.

Choose the extra base by the activities it unlocks rather than filling two nights for their own sake.

Read recent reviews for room condition, noise and after-hours check-in, then keep the best refundable choice.

For a short stay, compare buying with a local rental or a hotel room before adding storage to the family home.

Pick one lunch stop and one scenic pause; leaving room for those is usually more rewarding than chasing every lookout.

Check seasonal opening hours, fuel and road conditions on the less travelled sections before departure.

Spend several nights in one or two South West bases so the motorhome is not packed up every morning.

Choose the vehicle around luggage and route needs, then photograph it at collection and return.

Keep Rottnest as its own day and check ferry availability before building the rest of the schedule.

Confirm fuel, inspection and key-handover rules so the rental does not keep running after you leave the car.

Check whether island admission, bike hire and cancellation options are included before paying.

Compare cruise itineraries by actual ports and time ashore; a coastal voyage may not include the land sights you hoped to see.